Background: Oxygen (O-2) plays a critical role in the O-2-reduction reactions indispensable for life, but can produce free radicals that are involved in many diseases. Coenzyme Q(10) (CoQ(10)), acting as a redox carrier in the respiratory chain, occupies a central position in the energy metabolism and oxidative defence. Neonates seem to be very subjected to oxidative stress because of their deficient antioxidant systems. Design/Methods: The aim of the study was to verify whether the mode of delivery may affect CoQ10 levels in the mother and neonate, and thus influence the risk of oxidative damage in the newborn. We measured CoQ10 levels in maternal plasma and cord blood at birth after three different modes of delivery (45 term healthy pregnancies): (1) vaginal in room air (VD) (n = 15); (2) elective caesarean section with general anaesthesia (50% O-2 and 50% N2O) (CSg) (n = 15), and (3) elective caesarean section with spinal anaesthesia without O-2 (CSs) (n = 15). Our results showed higher levels of Q(10) in mothers and neonates with VD (1.29 +/- 0.43 and 0.15 +/- 0.06 mug/ml, respectively) or CSs (1.15 +/- 0.28 and 0.24 +/- 0.06 mug/ml, respectively) when compared to CSg (0.74 +/- 0.28 and 0.07 +/- 0.03 mug/ml, respectively) (p < 0.01). Conclusions: These data demonstrate that the mode of delivery may affect CoQ(10) levels in mothers and neonates, and thus influence the risk of oxidative damage in the newborn. Copyright (C) 2004 S. Karger AG, Basel.